Removal of Cr (VI) from aqueous solutions using peanut shell as adsorbent

The biosorption of Cr (VI) ions from aqueous solution by peanut shell (PNS) biosorbent was studied in a batch mode system. Factors affecting Cr (VI) biosorption such as pH (2-7), initial chromium ion concentrations (20-60 mg/l), contact time (6 h), adsorbent dosage (0.2-1.0 g) and temperature (293-313 K) were investigated. The adsorption equilibrium was established at 360 minutes. A comparison of the kinetic models has showed that pseudo-second order equation best described adsorption kinetics. Maximum adsorption was achieved at pH 2.0 and 3.0. The adsorption equilibrium data was fitted well to the Langmuir adsorption isotherm as compared to the Freundlich adsorption isotherm. The values of separation factor, R/sub L/ was found between 0.0235 and 0.0633 (0 < R/sub L/ < 1) which pointed out favorable adsorption of Cr (VI) on PNS adsorbent. The adsorption capacity was measured in terms of monolayer adsorption and was found to be 4.32 mg/g at 313 K. The thermodynamic parameters (ΔG, ΔH and ΔS) values indicated the endothermic, non spontaneous and entropy driven system of the adsorption process. (author)